4,5-Dialkoxy-2-hydroxybenzoic acid (3) is known as a raw material or synthesis intermediate of various pharmaceuticals and agricultural chemicals. In a known method for producing 4,5-dialkoxy-2-hydroxybenzoic acid (3), as shown in the following reaction scheme:
(wherein each of R1 and R2 represents a lower alkyl group), the methoxy group at the 2-position of 2,4,5-trialkoxybenzoic acid (a) is selectively demethylated by causing the acid to react with a Lewis acid in an ester, ketone, or amide solvent (Patent Document 1).